In this project, we are studying the expression of IL-4R and the role of IL-4 on solid human tumors. We have observed that human tumors of different histology also express IL-4R. Human breast carcinoma, ovarian carcinoma, melanoma and renal tumor lines, as well as fresh tumors obtained from the NCI, express high affinity IL-4R. The characteristics of these receptors appear to be similar to that reported on hematopoietic cells such as T cells, B cells, mast cells and macrophages. Human tumors also express a single species of mRNA of IL-4R. We are currently investigating the function of IL-4 on tumor cells. Our preliminary data indicate that IL-4 is directly growth inhibitory to some IL-4R positive tumor lines as tested by MTT assay. Furthermore, IL-4 appear to upregulate HLA-DR antigen on some tumor cells.